[ntp:questions] Does NTP cause an abrupt/sudden change in an orphan's system time?

unruh unruh at invalid.ca
Thu Aug 9 15:02:59 UTC 2012

On 2012-08-08, Rob <nomail at example.com> wrote:
> unruh <unruh at invalid.ca> wrote:
>> On 2012-08-08, Rob <nomail at example.com> wrote:
>>> Harlan Stenn <stenn at ntp.org> wrote:
>>>> If this situation is "difficult" for you I'd recommend you get an
>>>> inexpensive GPS receiver and use that to sync your master machine(s).
>>>> Check out the Sure Electronics GPS board, which can be easily modified
>>>> to provide a PPS signal.  There are other inexpensive GPS units as well.
>>> Yet another time the completely irrelevant topic of the hobbyist GPS
>>> receiver is brought into the thread...
>>> The OP was asking about abrupt/sudden changes in a system's time.
>>> This is unrelated to the availability of GPS.
>>> When he connects the GPS receiver he will have to watch the same issue
>>> as when connecting to another reference.
>> It was related to his statement that his server was not connected to the
>> net and thus its time was out, and then it connected to the net. The
>> statement about GPS was make to fix the problem that when it was not
>> connected to the net, it had a bad time. GPS "always" operates. Of
>> course his machine could be in a bunker 1000 meter underground with no
>> connection to the surface, in this case the GPS option would be no good
>> either. But in may circumstance it IS an answer to the problem the OP
>> had. 
> Of course not.   The OP wants to make sure his clock does not step
> when he starts ntpd.   When not configured correctly, the clock will
> step when ntpd is started.   It is too late to connect a GPS receiver
> now, he first needs to sort out how to get the clock adjusted without
> stepping.

No he wanted it not to step when the external net sources came online
after it had been operating in issolation for a long time. I agree that
we cannot change the past behaviour. We can however change the future
behaviour if this situation (isolated system which then connects with
external time sources). Using a gps so that the system is never
issolated is one way of solving the problem. It may not work in his
situation, which we know nothing about, but if he can get a gps signal
it will certainly solve the problem he was worried about. 

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